Non-aqueous electrolyte secondary battery

ABSTRACT

A non-aqueous electrolyte secondary battery includes a positive electrode, a negative electrode, a separator disposed between the both electrodes, a non-aqueous electrolytic solution and an exterior member made of a laminate material and housing the positive electrode, the negative electrode, the separator and the non-aqueous electrolytic solution. A polymeric support exists between the separator and at least one of the positive electrode and the negative electrode. Also, the separator contains polyethylene as a main component and contains not more than 10% by mass of polypropylene.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application claims priority to Japanese Patent ApplicationJP 2008-055507 filed in the Japan Patent Office on Mar. 5, 2008, theentire contents of which being incorporated herein by reference.

BACKGROUND

The present disclosure relates to a non-aqueous electrolyte secondarybattery and in more detail, to a non-aqueous electrolyte secondarybattery which is excellent in heat resistance, liquid-holding propertiesand cycle characteristic.

In recent years, a number of portable electronic devices, for example,camcorders (video tape recorders), cellular phones and portablecomputers, each achieving a reduction in size and weight, have appeared.Following this, development of batteries, in particular, secondarybatteries as a portable power source for such electronic devices hasbeen actively conducted. Above all, lithium ion secondary batteries haveattracted much attention as a device capable of realizing a high energydensity.

Also, recently, more reduction in size and weight and thinning of abattery is being advanced by using a laminated film or the like in placeof a metal-made battery can made of aluminum or iron as a batteryexterior material.

On the other hand, in order to increase the energy density, it isnecessary to charge a more amount of an active material which acts to acharge-discharge reaction. Following this, it is known that it isnecessary to use an electrolytic solution in an amount sufficient formoving a lithium ion between a positive electrode and a negativeelectrode. When the amount of the electrolytic solution is notsufficient, and the electrolytic solution does not completely fulfillthe surroundings of the active material, a portion which does not comeinto contact with the electrolytic solution does not react, and asufficient battery capacity is not obtainable.

Furthermore, as the repetition of charge and discharge proceeds, theelectrolytic solution is consumed between the positive electrode and thenegative electrode. Thus, the discharge capacity of the battery isgradually lowered before the positive electrode and negative electrodeactive materials have reached deterioration, thereby causing a problemof a lowering of the cycle characteristic or the generation of aninternal short circuit due to a shortage of the electrolytic solution.

In order to overcome such a problem, it is proposed that in a batteryusing a metal-made battery can, the cycle characteristic can be improvedby controlling the volume of a non-aqueous electrolytic solutionrelative to the discharge capacity (see, for example, JP-A-2-148576).

On the other hand, in order to meet the foregoing requirement forrealizing a high capacity of the battery, thinning of a separator isinevitable. However, the higher the capacity is, the larger the energyamount within the battery is. Therefore, at an abnormal time such asshort circuit and overcharge, the possibility of more excessivegeneration of heat generation than before is large.

For that reason, several kinds of means for securing safety even at anabnormal time are applied to the battery, and one of them is a shutdownfunction of the separator. The shutdown function is a function in whichwhen the temperature of the battery increases due to some factor, poresof the separator are clogged, and a battery reaction is stopped byinhibiting the movement of an ion, thereby suppressing the excessiveheat generation.

Polyethylene has been frequently used for a separator of a lithium ionsecondary battery because it is excellent in such a shutdown function.However, there may be the case where polyethylene is exposed to atemperature at which the shutdown function is revealed or higher. Inthat case, there was involved a problem that the separator causes heatshrinkage, and the exposed positive electrode and negative electrodecome into contact with each other to generate an internal short circuit,thereby causing thermorunaway.

On the other hand, polypropylene is exemplified as a material having ahigh melting point and capable of suppressing the heat shrinkage until ahigher temperature. However, inversely, the temperature at which theshutdown function is revealed becomes high.

Then, in order to solve these problems, a separator composed of alaminate of polyethylene and polypropylene is proposed (see, forexample, JP-A-10-261395).

In the foregoing problems of the related art, different from the case ofbatteries using the foregoing metal-made battery can, it is hard to saythat a lowering of the cycle characteristic or the generation of aninternal short circuit due to a shortage of the electrolytic solution issufficiently solved in a non-aqueous secondary battery using a laminatedfilm.

That is, when damaged, the laminated film is easily broken as comparedwith firm metal-made cans, and liquid leakage from a broken portionthereof is easy to occur. Accordingly, there was involved a problem thatwhen the amount of the electrolytic solution is increased for thepurpose of increasing the cycle characteristic, the liquid leakageeasily occurs.

On the other hand, in order that the revealment of a shutdown functionof a separator and the suppression of heat shrinkage properties may beregulated or made compatible with each other, when a laminate ofpolyethylene and polypropylene is used, the separator itself becomesthick. Thus, there was involved a problem that the energy density of thebattery is rather lowered.

In view of the foregoing problems of the related art, it is desirable toprovide a non-aqueous electrolyte secondary battery which is excellentin heat resistance, resistance to liquid leakage and cyclecharacteristic.

SUMMARY

In an embodiment, by arranging a prescribed polymeric support and byusing a separator in which polyethylene and polypropylene coexist in aprescribed ratio, accomplishment of the embodiment can be achieved.

That is, a non-aqueous electrolyte secondary battery according to anembodiment is a non-aqueous electrolyte secondary battery including apositive electrode, a negative electrode, a separator disposed betweenthe both electrodes, a non-aqueous electrolytic solution and an exteriormember made of a laminate material and housing the positive electrode,the negative electrode, the separator and the non-aqueous electrolyticsolution, wherein

a polymeric support exists between the separator and at least one of thepositive electrode and the negative electrode; and

the separator contains polyethylene as a main component and contains notmore than 10% by mass of polypropylene.

Also, in the non-aqueous electrolyte secondary battery according to theembodiment, it is preferable that the non-aqueous electrolytic solutionexisting in the non-aqueous electrolyte secondary battery is from 0.14to 0.35 g per cm3 of the volume of the non-aqueous electrolyte secondarybattery.

According to the embodiment, since not only the prescribed polymericsupport is arranged, but the separator in which polyethylene andpolypropylene coexist in a prescribed ratio, a non-aqueous electrolytesecondary battery which is excellent in heat resistance, resistance toliquid leakage and cycle characteristic can be provided.

Additional features and advantages are described herein, and will beapparent from the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is an exploded perspective view showing one example of a laminatetype battery which is a non-aqueous electrolyte secondary batteryaccording to an embodiment.

FIG. 2 is a schematic cross-sectional view of the battery element asshown in FIG. 1 along an II-II line thereof.

FIG. 3 is an exploded perspective view showing another example of alaminate type battery which is a non-aqueous electrolyte secondarybattery according to another embodiment.

FIG. 4 is an NMR chart used for the quantitative determination ofseparator components.

DETAILED DESCRIPTION

A non-aqueous electrolyte secondary battery according to an embodimentis hereunder described in detail.

FIG. 1 is an exploded perspective view showing one example of a woundbattery using a laminate material which is a non-aqueous electrolytesecondary battery according to an embodiment.

As shown in FIG. 1, this secondary battery is configured in such amanner that a wound battery element 20 having a positive electrodeterminal 11 and a negative electrode terminal 12 installed therein ischarged in the inside of an exterior member 30 (30A, 30B) in a filmstate. The positive electrode terminal 11 and the negative electrodeterminal 12 are each derived in, for example, the same direction fromthe inside towards the outside of the exterior member 30. The positiveelectrode terminal 11 and the negative electrode terminal 12 are eachconstituted of a metal material, for example, aluminum (Al), copper(Cu), nickel (Ni) and stainless steel.

The exterior member 30 is constituted of a rectangular laminated filmobtained by sticking, for example, a nylon film, an aluminum foil and apolyethylene film in this order. The exterior member 30 is, for example,provided in such a manner that the polyethylene film side and thebattery element 20 are disposed opposing to each other, and respectiveexternal edges thereof are joined with each other by fusion or anadhesive.

An adhesive film 31 is inserted between the exterior member 30 and eachof the positive electrode terminal 11 and the negative electrodeterminal 12 for the purpose of preventing invasion of the outside airfrom occurring. The adhesive film 31 is constituted of a material havingadhesiveness to the positive electrode terminal 11 and the negativeelectrode terminal 12, and for example, in the case where the positiveelectrode terminal 11 and the negative electrode terminal 12 are eachconstituted of the foregoing metal material, it is preferable that theadhesive film 31 is constituted of a polyolefin resin, for example,polyethylene, polypropylene, modified polyethylene and modifiedpolypropylene.

The exterior member 30 may also be constituted of a laminated filmhaving other structure, for example, a metal material-free laminatedfilm, a polymer film, for example, polypropylene or a metal film inplace of the foregoing laminated film.

Here, a general configuration of the exterior member can be expressed bya laminate structure of exterior layer/metal foil/sealant layer(however, the exterior layer and the sealant layer are sometimesconfigured of plural layers). In the foregoing example, the nylon filmis corresponding to the exterior layer, the aluminum foil iscorresponding to the metal foil, and the polyethylene film iscorresponding to the sealant layer.

It is sufficient that the metal foil functions as a barrier membranehaving water vapor permeation resistance. As the metal foil, not onlythe aluminum foil but a stainless steel foil, a nickel foil and a platediron foil are useful. Of these, the aluminum foil which is lightweightand excellent in workability can be favorably used.

Examples of a mode of the configuration (exterior layer/metalfoil/sealant layer) which can be used as the exterior member include Ny(nylon)/Al (aluminum)/CPP (cast polypropylene), PET (polyethyleneterephthalate)/Al/CPP, PET/Al/PET/CPP, PET/Ny/Al/CPP, PET/Ny/Al/Ny/CPP,PET/Ny/Al/Ny/PE (polyethylene), Ny/PE/Al/LLDPE (linear low densitypolyethylene), PET/PE/Al/PET/LDPE (low density polyethylene) andPET/Ny/Al/LDPE/CPP.

FIG. 2 is a schematic cross-sectional view showing the battery element20 as shown in FIG. 1 along an II-II line thereof. In FIG. 2, thebattery element 20 is one in which a positive electrode 21 and anegative electrode 22 are disposed opposing to each other and wound viaa polymeric support (as described later) 23 which holds a non-aqueouselectrolytic solution therein and a separator 24, and an outermostperiphery thereof is protected by a protective tape 25.

Here, FIG. 3 shows an exploded perspective view showing a non-aqueouselectrolyte secondary battery according to another embodiment. That is,FIG. 3 is an exploded perspective view showing a laminate type batteryusing a laminate material which is a non-aqueous electrolyte secondarybattery according to another embodiment. Members which are substantiallythe same as those in the foregoing wound secondary battery are given thesame symbols, and descriptions thereof are omitted.

As shown in FIG. 3, this battery has the same configuration as in thewound battery as shown in FIG. 1, except that a laminated batteryelement 20′ is provided in place of the foregoing wound battery element20.

The laminated battery element 20′ has a laminate structure in which apositive electrode and a negative electrode in a sheet form are disposedopposing to each other via the foregoing polymeric support which holds anon-aqueous electrolytic solution therein and a separator, and forexample, the negative electrode sheet, the polymeric support layer, theseparator, the polymeric support layer and the positive electrode sheetare laminated in this order.

In the embodiment as shown in FIG. 3, the laminated battery element 20′is one in which a negative electrode in a sheet form (negative electrodesheet) and a positive electrode in a sheet form (positive electrodesheet) are alternately laminated via a separator. Then, a polymericsupport is further arranged between the positive electrode sheet and theseparator and between the negative electrode sheet and the separator,respectively.

The laminated battery element 20′ has a configuration substantially thesame as in the wound battery as shown in FIG. 1 except for the foregoingpoint. Therefore, the description of the non-aqueous electrolytesecondary battery according to an embodiment is continued while againreferring to the foregoing wound battery.

As shown in FIG. 2, the positive electrode 21 has, for example, astructure in which a positive electrode active material layer 21B iscoated on one or both surfaces of a positive electrode collector 21Ahaving a pair of opposing surfaces. The positive electrode collector 21Ahas a portion which is exposed without being coated with the positiveelectrode active material layer 21B in one end in the longitudinaldirection thereof, and the positive electrode terminal 11 is installedin this exposed portion.

The positive electrode collector 21A is constituted of a metal foil, forexample, an aluminum foil, a nickel foil and a stainless steel foil.

The positive electrode active material layer 21B contains, as a positiveelectrode active material, any one kind or two or more kinds of apositive electrode material capable of intercalating and deintercalatinga lithium ion and may contain a conductive agent and a binder as theneed arises.

Examples of the positive electrode material capable of intercalating anddeintercalating lithium include lithium-free chalcogen compounds(especially, layered compounds and spinel type compounds), for example,sulfur (S), iron disulfide (FeS2), titanium disulfide (TiS2), molybdenumdisulfide (MoS2), niobium diselenide (NbSe2), vanadium oxide (V2O5),titanium dioxide (TiO2) and manganese dioxide (MnO2); lithium-containingcompounds containing lithium therein; and conductive polymer compounds,for example, polyaniline, polythiophene, polyacetylene and polypyrrole.

Of these, lithium-containing compounds are preferable because theyinclude ones capable of obtaining high voltage and high energy density.Examples of such a lithium-containing compound include complex oxidescontaining lithium and a transition metal element; and phosphatecompounds containing lithium and a transition metal. From the viewpointof obtaining a higher voltage, those containing cobalt (Co), nickel(Ni), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), chromium (Cr),vanadium (V), titanium (Ti) or an arbitrary mixture thereof arepreferable.

Such a lithium-containing compound is representatively represented bythe following general formula (1) or (2):

LixMIO2   (1)

LiyMIIPO4   (2)

In the foregoing formula, MI and MII each represents one or more kindsof a transition metal element; and values of x and y vary depending uponthe charge-discharge state of the battery and are usually satisfied with0.05≦×≦1.10 and 0.05≦y≦1.10, respectively.

The compound of the formula (1) generally has a layered structure; andthe compound of the formula (2) generally has an olivine structure.

Also, specific examples of the complex oxide containing lithium and atransition metal element include a lithium cobalt complex oxide(LixCoO2), a lithium nickel complex oxide (LixNiO2), lithium nickelcobalt complex oxide (LixNi1-zCozO2) (0<z<1)) and a lithium manganesecomplex oxide having a spinel structure (LiMn2O4).

Specific examples of the phosphate compound containing lithium and atransition metal element include a lithium iron phosphate compoundhaving an olivine structure (LiFePO4) and a lithium iron manganesephosphate compound (LiFe1-vMnvPO4 (v<1)).

In these complex oxides, for the purpose of stabilizing the structure orthe like, ones in which a part of the transition metal is substitutedwith Al, Mg or other transition metal element or contained in a crystalgrain boundary and ones in which a part of oxygen is substituted withfluorine, etc, can be exemplified. Furthermore, at least a part of thesurface of the positive electrode active material may be coated withother positive electrode active material. Also, a mixture of pluralkinds of materials may be used as the positive electrode activematerial.

On the other hand, likewise the positive electrode 21, the negativeelectrode 22 has, for example, a structure in which a negative electrodeactive material layer 22B is provided on one or both surfaces of anegative electrode collector 22A having a pair of opposing surfaces. Thenegative electrode collector 22A has a portion which is exposed withoutbeing provided with the negative electrode active material layer 22B inone end in the longitudinal direction thereof, and the negativeelectrode terminal 12 is installed in this exposed portion.

The negative electrode collector 22A is constituted of a metal foil, forexample, a copper foil, a nickel foil and a stainless steel foil.

The negative electrode active material layer 22B contains, as a negativeelectrode active material, any one kind or two or more kinds of anegative electrode material capable of intercalating and deintercalatinga lithium ion and a metal lithium and may contain a conductive agent anda binder as the need arises.

Examples of the negative electrode material capable of intercalating anddeintercalating lithium include carbon materials, metal oxides andpolymer compounds. Examples of the carbon material include hardlygraphitized carbon materials, artificial graphite materials and graphitebased materials. More specific examples thereof include pyrolyticcarbons, cokes, graphites, vitreous carbons, organic polymer compoundburned materials, carbon fibers, active carbon and carbon black.

Of these, examples of the cokes include pitch coke, needle coke andpetroleum coke. The organic polymer compound burned material as referredto herein is a material obtained through carbonization by burning apolymer material, for example, phenol resins and furan resins at anappropriate temperature. Also, examples of the metal oxide include ironoxide, ruthenium oxide and molybdenum oxide; and examples of the polymercompound include polyacetylene and polypyrrole.

Furthermore, examples of the negative material capable of intercalatingand deintercalating lithium include materials containing, as aconstitutional element, at least one of metal elements and semi-metalelements capable of forming an alloy together with lithium. Thisnegative electrode material may be a single body, an alloy or a compoundof a metal element or a semi-metal element. Also, one having a singlekind or plural kinds of a phase in at least a part thereof may be used.

In an embodiment, the alloy also includes an alloy containing a singlekind or plural kinds of a metal element and a single kind or pluralkinds of a semi-metal element in addition to alloys composed of pluralkinds of a metal element. Also, the alloy may contain a non-metalelement. Examples of its texture include a solid solution, a eutectic(eutectic mixture), an intermetallic compound and one in which pluralkinds thereof coexist.

Examples of the metal element or semi-metal element include tin (Sn),lead (Pb), aluminum, indium (In), silicon (Si), zinc (Zn), antimony(Sb), bismuth (Bi), gallium (Ga), germanium (Ge), arsenic (As), silver(Ag), hafnium (Hf), zirconium (Zr) and yttrium (Y).

Above all, a metal element or a semi-metal element belonging to theGroup 14 of the long form of the periodic table is preferable; andsilicon or tin is especially preferable. This is because silicon and tinhave a large ability to intercalate and deintercalate lithium and areable to obtain a high energy density.

Examples of alloys of tin include alloys containing, as a secondconstitutional element other than tin, at least one member selected fromthe group consisting of silicon, magnesium (Mg), nickel, copper, iron,cobalt, manganese, zinc, indium, silver, titanium (Ti), germanium,bismuth, antimony and chromium (Cr).

Examples of alloys of silicon include alloys containing, as a secondconstitutional element other than silicon, at least one member selectedfrom the group consisting of tin, magnesium, nickel, copper, iron,cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth,antimony and chromium.

Examples of compounds of tin or silicon include compounds containingoxygen (O) or carbon (C), and these compounds may contain the foregoingsecond constitutional element in addition to tin or silicon.

Next, the polymeric support layer 23 has ion conductivity and is able tohold a non-aqueous electrolytic solution therein. In the embodiment asshown in FIG. 2, this polymeric support layer 23 comes into closecontact with or adheres to the separator 24. The polymeric support layer23 may come into close contact with or adhere to the separator and theelectrode as in the separator 24 and the positive electrode 21 or theseparator 24 and the negative electrode 22. Alternatively, the polymericsupport layer 23 may not come into close contact with or adhere to theseparator but come into close contact with or adhere to either one orboth of the positive electrode 21 and the negative electrode 22.

It is meant by the terms “close contact” as referred to herein that thepolymeric support layer 23 comes into contact with the separator 24 orthe positive electrode 21 or the negative electrode 22 closely to anextent that they do not relatively move each other unless a prescribedforce is added.

When the polymeric support layer 23 and the separator 24, or thepolymeric support layer 23 and the positive electrode or negativeelectrode come into close contact with or adhere to each other, thepolymeric support layer 23 holds a non-aqueous electrolytic solutiontherein and becomes a gel non-aqueous electrolyte layer, whereby thepositive electrode 21 or the negative electrode 22 and the separator 24are adhered to each other via this non-aqueous electrolyte layer.

The degree of this adhesion is preferably a degree such that, forexample, a peel strength between the separator and the exposed portionof the positive electrode 21 or the negative electrode 22 where theactive material layer is not provided, but the collector is exposed is 5mN/mm or more. The peel strength is an average value of the forcerequired to peel the collector disposed on s stage from the separatorwhile pulling at a rate of 10 cm/min in the 180° direction within a timeperiod of from 6 seconds to 25 seconds after start of the pulling.

By such close contact or adhesion, in the non-aqueous electrolytesecondary battery according to an embodiment, an excess of thenon-aqueous electrolytic solution which does not substantiallycontribute to a battery reaction can be reduced, and the non-aqueouselectrolytic solution is efficiently supplied into the surroundings ofthe electrode active material. Accordingly, the non-aqueous electrolytesecondary battery according to an embodiment exhibits an excellent cyclecharacteristic even with a smaller amount of the non-aqueouselectrolytic solution than that of the related art. Also, since theamount of the non-aqueous electrolytic solution to be used is small, theresistance to liquid leakage is excellent.

The polymeric support which constitutes the foregoing polymeric supportlayer is not particularly limited so far as it holds the non-aqueouselectrolytic solution therein, thereby exhibiting ion conductivity.Examples thereof include acrylonitrile based polymers having acopolymerization amount of acrylonitrile of 50% by mass or more, andespecially 80% by mass or more, aromatic polyamides,acrylonitrile/butadiene copolymers, acrylic polymers composed of anacrylate or methacrylate homopolymer or copolymer, acrylamide basedpolymers, fluorine-containing polymers of vinylidene fluoride, etc.,polysulfones and polyarylsulfones. In particular, a polymer having acopolymerization amount of acrylonitrile of 50% by mass or more has a CNgroup in a side chain thereof, and thus, it has a high dielectricconstant and is able to form a polymeric gel electrolyte with high ionconductivity.

In order to enhance the supporting properties of the non-aqueouselectrolytic solution relative to such a polymer or enhance the ionconductivity of the polymeric gel electrolyte from such a polymer,copolymers obtained by copolymerizing acrylonitrile with a vinylcarboxylic acid (for example, acrylic acid, methacrylic acid anditaconic acid), acrylamide, methacrylsufonic acid, a hydroxyalkyleneglycol (meth)acrylate, an alkoxyalkylene glycol (meth)acrylate, vinylchloride, vinylidene chloride, vinyl acetate, a (meth)acrylate of everysort, etc. in a proportion of preferably not more than 50% by mass, andespecially not more than 20% by mass can be used.

Also, the aromatic polyamide is a high heat-resistant polymer. Thus,when a polymeric gel electrolyte which is required to have high heatresistance as in automobile batteries is required, the aromaticpolyamide is a preferred polymer compound. A polymer having acrosslinking structure which is obtained through copolymerization withbutadiene, etc. can also be used.

In particular, polymers containing, as a constitutional component,vinylidene fluoride, namely homopolymers, copolymers and multi-componentcopolymers are preferable as the polymeric support. Specific examplesthereof include polyvinylidene fluoride (PVdF), a polyvinylidenefluoride-hexafluoropropylene copolymer (PVdF-HFP) and a polyvinylidenefluoride-hexafluoropropylene-chlorotrifluoroethylene copolymer(PVdF-HEP-CTFE).

Next, the separator 24 is usually composed of an insulating thinmembrane having high ion permeability and predetermined mechanicalstrength, such as a porous membrane composed of a polyolefin based resinor a porous membrane composed of an inorganic material such as a ceramicnon-woven fabric, or the like. However, in the non-aqueous electrolytesecondary battery according to the present embodiment, the separator 24is configured of a porous membrane containing polyethylene as a maincomponent and containing not more than 10% by mass of polypropylene.

Here, in the separator in which polyethylene and polypropylene coexist,since a melting point of polypropylene is higher than that ofpolyethylene, the start temperature of heat shrinkage can be shifted toa higher temperature side. Inversely, since a shutdownfunction-revealing temperature of polypropylene is high, the batterytemperature at the time of overcharge or internal short circuit is easyto become high, and therefore, thermorunaway is easily caused.

According to an embodiment, by making a mixing ratio of polyethylene andpolypropylene fall within the foregoing range, the start temperature ofheat shrinkage can be increased while keeping the shutdownfunction-revealing temperature low.

While the start temperature of heat shrinkage is low as compared withthe case of 100% by mass of polypropylene, according to an embodiment,the separator and the electrode are firmly adhered to each other by theforegoing polymeric support, and therefore, it is possible to adequatelycontrol the heat shrinkage. Furthermore, according to such a structurewhere the polymeric support is arranged, since the separator itself canbe made thin, the energy density of the battery can be kept high.

Also, as constitutional components of the foregoing separator, it ispreferable to choose polyethylene having a melting point of from about130 to 140° C. and polypropylene having a melting point of from about160 to 170° C.

When a material having an excessively low melting point is contained asthe constitutional component of the separator, a temperature at whichthe separator fuses is low so that the useful temperature becomes low.On the other hand, when a material having an excessively high meltingpoint is contained as the constitutional component of the separator, atemperature at which the separator reveals the shutdown function is highso that thermorunaway is possibly caused, whereby there may be the casewhere it is difficult to secure the safety. Also, when there is adifference in melting point of 20° C. or more between the pluralconstitutional components, the functions including both shutdown andavoidance of the heat shrinkage can be sufficiently obtained.

A thickness of the separator is preferably from 5 to 20 μm.

Next, the non-aqueous electrolytic solution may be any solutioncontaining an electrolyte salt and a non-aqueous solvent.

Here, the electrolyte salt may be any salt capable of generating an ionupon being dissolved or dispersed in a non-aqueous solvent as describedlater. Though lithium hexafluorophosphate (LiPF6) can be favorably used,the electrolyte salt is not limited thereto.

That is, inorganic lithium salts, for example, lithium tetrafluoroborate(LiBF4), lithium hexafluoroarsenate (LiAsF6), lithiumhexafluoroantimonate (LiSbF6), lithium perchlorate (LiClO4) and lithiumtetrachloroaluminate (LiAlCl4); lithium salts of aperfluoroalkanesulfonate derivative, for example, lithiumtrifluoromethanesulfonate (LiCF3SO3), lithiumbis(trifluoromethanesulfone)imide (LiN(CF3SO2)2), lithiumbis(pentafluoromethanesulfone)imide (LiN(C2F5SO2)2) and lithiumtris(trifluoromethanesulfone)methide (LiC(CF3SO2)3) can be used. Thesesalts can be used singly or in combination of two or more kinds thereof.

The content of such an electrolyte salt is preferably from 5 to 25% bymass. When the content of such an electrolyte salt is less than 5% bymass, there is a possibility that sufficient conductivity is notobtainable. On the other hand, when it exceeds 25% by mass, there is apossibility that the viscosity excessively increases.

Also, examples of the non-aqueous solvent include varioushigh-dielectric solvents and low-viscosity solvents.

Ethylene carbonate or propylene carbonate or the like can be favorablyused as the high-dielectric solvent, but the high-dielectric solvent isnot limited thereto. Other examples of the high-dielectric solventinclude cyclic carbonates, for example, butylene carbonate, vinylenecarbonate, 4-fluoro-1,3-dioxolan-2-one (fluoroethylene carbonate),4-chloro-1,3-dioxolan-2-one (chloroethylene carbonate) andtrifluoromethylethylene carbonate.

Also, in place of or in addition to the cyclic carbonate, a lactone, forexample, γ-butyrolactone and γ-valerolactone, a lactam, for example,N-methylpyrrolidone, a cyclic carbamic ester, for example,N-methyloxazolidinone, a sulfone compound, for example, tetramethylenesulfone or the like can be used as the high-dielectric solvent.

On the other hand, diethyl carbonate can be favorably used as thelow-viscosity solvent. Besides, chain carbonates, for example, dimethylcarbonate, ethyl methyl carbonate and methyl propyl carbonate; chaincarboxylic esters, for example, methyl acetate, ethyl acetate, methylpropionate, ethyl propionate, methyl butyrate, methyl isobutyrate,methyl trimethylacetate and ethyl trimethylacetate; chain amides, forexample, N,N-dimethylacetamide; chain carbamic esters, for example,methyl N,N-diethylcarbamate and ethyl N,N-diethylcarbamate; and ethers,for example, 1,2-dimethoxyethane, tetrahydrofuran, tetrahydropyran and1,3-dioxolane.

As the non-aqueous electrolytic solution to be used in the non-aqueouselectrolyte secondary battery according to an embodiment, the foregoinghigh-dielectric solvent and low-viscosity solvent can be used singly orin admixture of two or more kinds thereof at any desired mixing ratio.Preferably, the non-aqueous electrolytic solution contains from 20 to50% by mass of a cyclic carbonate and from 50 to 80% by mass of alow-viscosity solvent (low-viscosity non-aqueous solvent). Inparticular, a chain carbonate having a boiling point of not higher than130° C. is desirably used as the low-viscosity solvent. By using such anon-aqueous electrolytic solution, the polymeric support can befavorably swollen with a small amount of the non-aqueous electrolyticsolution, and it is possible to devise to make both suppression ofswelling or prevention of the leakage of the battery and highconductivity much more compatible with each other.

When the ratio of the cyclic carbonate to the low-viscosity solventfalls outside the foregoing range, there is a possibility that theconductivity of the electrolytic solution is lowered, and the cyclecharacteristic is lowered.

Examples of the chain carbonate having a boiling point of not higherthan 130° C. include dimethyl carbonate, ethyl methyl carbonate anddiethyl carbonate.

Also, what a halogen atom-containing cyclic carbonic ester derivative iscontained as the foregoing cyclic carbonate in the non-aqueouselectrolytic solution is more preferable because the cycliccharacteristic is improved.

Examples of such a cyclic carbonic ester derivative include4-fluoro-1,3-dioxolan-2-one and 4-chloro-1,3-dioxolan-2-one. Thesecyclic carbonic ester derivatives can be used singly or in combination.

The content of the cyclic carbonic ester derivative is preferably from0.5 to 2% by mass. When the content of the cyclic carbonic esterderivative is too low, an effect for enhancing the cyclic characteristicis small, whereas when it is too high, there is a possibility thatswelling at the time of high-temperature storage becomes large.

According to an embodiment, since the amount of the non-aqueouselectrolytic solution existing between the polymeric support layer andthe separator, the positive electrode or the negative electrode withoutbeing supported by any of them is low, even when the low-viscositysolvent having a low boiling point is used in an amount of 50% by massor more is used, the swelling is suppressed on a low level.

In the non-aqueous electrolyte secondary battery according to anembodiment as described previously, the non-aqueous electrolyticsolution existing within the battery, typically the pouring amount ofthe non-aqueous electrolytic solution is preferably from 0.14 to 0.35 gper cm3 of the volume of this non-aqueous electrolyte secondary battery.

When the pouring amount of the non-aqueous electrolytic solution is lessthan 0.14 g per cm3 of the volume of the battery, there is a possibilitythat expected battery performances, specifically expected initialcharge-discharge capacity and capacity retention rate cannot berealized, whereby when it exceeds 0.35 g, there is a possibility thatthe resistance to liquid leakage is lowered.

Here, the pouring amount within the battery is, for example, measured bya method as described below.

First of all, a weight of the battery is measured; and subsequently, thebattery element is taken out and then disassembled into the positiveelectrode, the negative electrode and the separator. Thereafter, thepositive electrode, the negative electrode, the separator and theexterior member are immersed in a dimethyl carbonate solution for 2days; and after filtration, vacuum drying is carried out for 3 days. Avalue obtained by subtracting the weight after vacuum drying from theinitial weight is defined as the pouring amount.

Also, in the non-aqueous electrolyte secondary battery according to thepresent embodiment, it is preferable that a ratio (MO/MA) of the amountMO of the non-aqueous electrolytic solution existing between the batteryelement 20 and the exterior member 30 to the amount MA of thenon-aqueous electrolytic solution existing inside the exterior member 30is not more than 0.04.

When the thus defined MO/MA exceeds 0.04, there is a possibility thatswelling of the battery at the time of high-temperature storage cannotbe sufficiently suppressed. Also, it is preferable that the MO/MA valueis small as far as possible. Most desirably, the MO/MA value is 0.However, even when it is not more than 0.03, a more remarkable effectfor suppressing swelling can be obtained.

Here, the amount MA of the non-aqueous electrolytic solution existinginside the exterior member, namely within the non-aqueous electrolytesecondary battery may be, for example, measured and calculated in thefollowing method.

First of all, a mass of the battery is measured; and subsequently, thebattery element is taken out and then disassembled into the positiveelectrode, the negative electrode and the separator. Next, the positiveelectrode, the negative electrode, the separator and the exterior memberare immersed in a rinse liquid such as dimethyl carbonate for 2 days;and after filtration, vacuum drying is carried out for 3 days.Thereafter, a mass of the battery after vacuum drying is measured, andthe mass of the battery after vacuum drying is subtracted from theinitial mass of the battery, thereby determining MA.

On the other hand, the amount MO of the non-aqueous electrolyticsolution existing between the battery element and the exterior member,namely existing within the battery and outside the battery element maybe, for example, measured and calculated in the following method.

First of all, a mass of the battery is measured, and the battery elementis then taken out. Subsequently, the thus taken out battery element isinterposed by a raw material capable of absorbing the non-aqueouselectrolytic solution therein, for example, cloths, and all of thenon-aqueous electrolytic solutions which have oozed out upon applicationof a load of 10 kPa are wiped off. Also, the exterior member from whichthe battery element has been taken out is immersed in a rinse liquidsuch as dimethyl carbonate and then dried. Thereafter, a total mass ofthe exterior member and the battery element having been subjected to awiping-off treatment is measured, and the total mass of the exteriorbody and the electrode body after the wiping-off treatment is subtractedfrom the initial mass of the battery, thereby determining MO.

Next, one example of the manufacturing method of the foregoing secondarybattery is described.

The foregoing laminate type secondary battery can be manufactured in thefollowing manner.

First of all, the positive electrode 21 is prepared. For example, incase of using a granular positive electrode active material, a positiveelectrode active material and optionally, a conductive agent and abinder are mixed to prepare a positive electrode mixture, which is thendispersed in a dispersion medium, for example, N-methyl-2-pyrrolidone toprepare a positive electrode mixture slurry.

Subsequently, this positive electrode mixture slurry is coated on thepositive electrode collector 21A and dried, and then compression moldedto form the positive electrode active material layer 21B.

Also, the negative electrode 22 is prepared. For example, in case ofusing a granular negative electrode active material, a negativeelectrode active material and optionally, a conductive agent and abinder are mixed to prepare a negative electrode mixture, which is thendispersed in a dispersion medium such as N-methyl-2-pyrrolidone toprepare a negative electrode mixture slurry. Thereafter, this negativeelectrode mixture slurry is coated on the negative electrode collector22A and dried, and then compression molded to form the negativeelectrode active material layer 22B.

The polymeric support layer 23 is then formed on the separator 24.Examples of the technique for forming the polymeric support layer 23 onthe separator 24 include a technique of coating a polymericsupport-containing solution on the surface of the separator 24 andremoving the solvent; and a technique of affixing a separately preparedpolymeric support layer on the surface of the separator 24.

Examples of the technique for coating the polymeric support-containingsolution on the surface of the separator 24 include a technique ofimmersing the separator in the polymeric support-containing solution; atechnique of supplying and coating the solution by means of a T-dieextrusion method or the like; and a technique of coating the solution onthe surface of a base material by a spraying method or with a rollcoater, a knife coater, or the like.

Examples of the technique of a desolvation treatment for removing thesolvent include a technique of removing the solvent by drying; atechnique of immersing the coated layer in a poor solvent of thepolymeric support to remove the solvent by extraction and then dryingand removing the poor solvent; and a combination of these techniques.

As the technique of affixing the separately prepared polymeric supportlayer to the surface of the separator 24, the adhesion can be achievedby using an adhesive. In that case, however, the adhesive may beadequately chosen according to the type of the electrolytic solution tobe used (for example, an acid, an alkali and an organic solvent), andattention may be paid not so as to generate clogging.

Examples of technique for allowing the polymeric support layer to comeinto close contact with the separator include heat fusion at atemperature of the gel transition point or higher. In particular, heatfusion while applying a pressure, for example, hot roll compression ispreferable.

Subsequently, the positive electrode terminal 11 is installed in thepositive electrode 21, and the negative electrode terminal 12 is alsoinstalled in the negative electrode 22. Thereafter, the separator 24provided with the polymeric support layer 23, the positive electrode 21,another separator 24 of the same type and the negative electrode 22 aresuccessively laminated and wound. The protective tape 25 is adhered ontothe outermost peripheral portion to form a wound electrode body.Furthermore, the wound electrode body is interposed between the exteriormembers 30 (30A and 30B), and the peripheral portions thereof are heatfused with each other except for one side, thereby forming a bag.

Thereafter, an electrolyte salt such as lithium hexafluorophosphate anda non-aqueous electrolytic solution containing a non-aqueous solventsuch as ethylene carbonate are prepared and poured into the inside ofthe wound electrode body from an opening of the exterior member 30. Theopening of the exterior member 30 is heat fused to achieve hermeticsealing. According to this, the non-aqueous electrolytic solution isheld by the polymeric support layer 23, thereby completing the secondarybattery as shown in FIGS. 1 and 2.

In the technique of swelling the electrolytic solution to form anelectrolyte after the polymeric support layer is formed and contained, aprecursor which is a raw material for forming the polymeric support andthe solvent can be removed in advance so that such a material or solventdoes not remain within the electrolyte. Furthermore, the process offorming the polymeric support can be favorably controlled. For thatreason, it is possible to make the polymeric support layer come intoclose contact with the separator, the positive electrode and/or thenegative electrode.

In the secondary battery as described previously, when charged, alithium ion is deintercalated from the positive electrode activematerial layer 21B and intercalated in the negative electrode activematerial layer 22B via the non-aqueous electrolytic solution held in thepolymeric support layer 23. When discharged, a lithium ion isdeintercalated from the negative electrode active material layer 22B andintercalated in the positive electrode active material layer 21B via thepolymeric support layer 23 and the non-aqueous electrolytic solution.

EXAMPLES

An embodiment is hereunder described in more detail with reference tothe following Examples and Comparative Examples while referring to theaccompanying drawings. However, it should not be construed that thepresent invention is limited thereto.

Example 1-1

Cobalt carbonate (CoCO3) was mixed in a proportion of 1 mole per 0.5moles of lithium carbonate (Li2CO3), and the mixture was burned in airat 900° C. for 5 hours, thereby obtaining a lithium cobalt complex oxide(LiCoO2) as a positive electrode active material.

Subsequently, 85 parts by mass of the obtained lithium cobalt complexoxide, 5 parts by mass of graphite as a conductive agent and 10 parts bymass of polyvinylidene fluoride as a binder were mixed to prepare apositive electrode mixture, which was then dispersed inN-methyl-2-pyrrolidone as a dispersion medium to form a positiveelectrode mixture slurry. Subsequently, this positive electrode mixtureslurry was uniformly coated on the both surfaces of the positiveelectrode collector 21A composed of an aluminum foil and having athickness of 20 μm, dried and then compression molded by a roll press toform the positive electrode active material layer 21B. There was thusprepared the positive electrode 21. Thereafter, the positive electrodeterminal 11 was installed in the positive electrode 21.

On the other hand, a pulverized graphite powder was prepared as anegative electrode active material. 90 parts by mass of this graphitepowder and 10 parts by mass of polyvinylidene fluoride as a binder weremixed to prepare a negative electrode mixture, which was then dispersedin N-methyl-2-pyrrolidone as a dispersion medium to form a negativeelectrode mixture slurry.

Subsequently, this negative electrode mixture slurry was uniformlycoated on the both surfaces of the negative electrode collector 22Acomposed of a copper foil and having a thickness of 15 μm, dried andthen compression molded by a roll press to form the negative electrodeactive material layer 22B. There was thus prepared the negativeelectrode 22. Subsequently, the negative electrode terminal 12 wasinstalled in the negative electrode 22.

Also, polyvinylidene fluoride was used as a polymer compound to be usedfor the polymeric support layer 23. A solution of the subject polymerprepared by dissolving it in an N-methyl-2-pyrrolidone solution in anamount of 12 parts by mass was coated on the both surface of theseparator 24 composed of a microporous film and having a thickness of 12μm by a coating unit. On that occasion, a ratio of polyethylene (meltingpoint: 135° C.) and polypropylene (melting point: 165° C.) as materialsof the separator was changed as shown in Table 1.

This coated film was immersed in deionized water and then dried to formthe polymeric support layer 23 having a thickness of 5 μm on theseparator 24.

The quantitative determination of the composition of the used separatorwas carried out in the following manner.

<Measurement Condition>

Apparatus: Bruker's nuclear magnetic resonance apparatus, AVANCE II 400(equipped with a 4-mm MAS probe)

Temperature: Room temperature

Measurement nucleus: 13C

Measurement method: CPMAS method (cross-polarization magic anglespinning method)

Contact time: 0.4 ms

Rotation rate of sample: 10 kHz

Standard material: 1M-LiCl aq

<Measurement Method>

A standard sample of PP/PE=1/1 (molar number ratio of monomers) wassubjected to 13C CPMAS NMR spectral measurement at a rotation rate ofthe sample of 10 kHz for a contact time of 0.4 ms, thereby estimating adifference in magnetization transfer efficiency of the respectivecomponents. By determining a coefficient for correcting it, an actualsample measured under the same condition was quantitatively determined.With respect to the obtained NMR spectra, an area ratio of eachcomponent was adopted as a composition ratio (see FIG. 4).

The thus prepared positive electrode 21 and negative electrode 22 werebrought into close contact with each other via the separator 24 havingthe polymeric support layer 23 formed thereon and wound in thelongitudinal direction. The protective tape 25 was stuck on theoutermost periphery to prepare the wound battery element 20.

Furthermore, the prepared battery element 20 was interposed by theexterior members 30A and 30B, and three sides thereof were heat fused. Amoisture-resistant aluminum laminated film prepared by laminating a 25μm-thick nylon film, a 40 μm-thick aluminum foil and a 30 μm-thickpolypropylene film in this order from the outermost layer was used asthe exterior member 30 (30A, 30B).

Subsequently, an electrolytic solution was poured into the exteriormember 30 having the battery element 20 contained therein, and theremaining one side of the exterior member 30 was heat fused under areduced pressure, thereby achieving hermetic sealing. On that occasion,the remaining one side of the exterior member 30 was heat fused andhermetically sealed so as to have a prescribed amount of theelectrolytic solution as shown in Table 1 (weight of the electrolyticsolution within the cell) relative to the cell volume as an inner volumeof the exterior member 30.

An electrolytic solution prepared by dissolving 1.2 moles/L of lithiumhexafluorophosphate in a mixed solvent of ethylene carbonate anddiethylene carbonate in a mass ratio of ethylene carbonate to diethylenecarbonate of 3/7 was used as the electrolytic solution.

Thereafter, the obtained sealed body was interposed by iron plates andheated at 70° C. for 3 minutes, thereby adhering the separator 24 toeach of the positive electrode 21 and the negative electrode 22 via thepolymeric support layer 23. There was thus obtained a non-aqueouselectrolyte secondary battery of this Example having a size of 5 mm inthickness×30 mm in width×40 mm in height (6 cm3) as shown in FIGS. 1 and2.

Examples 1-2 to 1-6

Non-aqueous electrolyte secondary batteries of these Examples were eachobtained by repeating the same operations as in Example 1, except forregulating the composition of the separator material as shown in Table1.

Comparative Examples 1-1 to 1-5

Non-aqueous electrolyte secondary batteries of these ComparativeExamples were each obtained by repeating the same operations as inExample 1, except for regulating the composition of the separatormaterial as shown in Table 1.

Comparative Example 1-6

A non-aqueous electrolyte secondary batter of this Comparative Examplewas obtained by repeating the same operations as in Example 1, exceptfor not forming the polymeric support.

<Initial Discharge Capacity>

Each of the secondary batteries of Examples 1-1 to 1-6 and ComparativeExamples 1-1 to 1-6 was subjected to constant-current constant-voltagecharge at 23° C. and 200 mA for 7 hours until it reached an upper limitof 4.2 V and then subjected to constant-current discharge at 100 mAuntil it reached a final voltage of 2.5 V, thereby determining aninitial discharge capacity. The obtained results are shown in Table 1.

<Safety Test by Nail Piercing>

Each of the secondary batteries of Examples 1-1 to 1-6 and ComparativeExamples 1-1 to 1-6 was charged to 4.25 V; and thereafter, a barrel ofthe battery was pieced and penetrated by a nail having a diameter of 2.5mm at a rate of 100 mm/sec in the state of keeping the batterytemperature at 25° C., thereby measuring a maximum attained temperatureof the battery. The obtained results are shown in Table 1.

<Measurement of Weight of Electrolytic Solution in Battery>

Each of the secondary batteries of Examples 1-1 to 1-6 and ComparativeExamples 1-1 to 1-6 was measured for a weight of the electrolyticsolution in the battery.

That is, with respect to each secondary battery, after measuring aweight of the battery, the battery element is taken out and thendisassembled into the positive electrode, the negative electrode and theseparator. Thereafter, the positive electrode, the negative electrode,the separator and the exterior member are immersed in a dimethylcarbonate solution for 2 days; and after filtration, vacuum drying iscarried out for 3 days. The weight of the electrolytic solution wasobtained by subtracting the weight after vacuum drying from the initialweight. The obtained results are shown in Table 1.

TABLE 1 Presence or absence Composition of separator Initial MaximumAmount of of material discharge attained electrolytic polymericPolyethylene Polypropylene capacity temperature solution support (%) (%)(mAh) (° C.) (g) Example 1-1 Yes 95 5 852 64 1.6 Example 1-2 Yes 99.50.5 854 98 1.6 Example 1-3 Yes 99 1 852 85 1.6 Example 1-4 Yes 97 3 85168 1.6 Example 1-5 Yes 92 8 853 88 1.6 Example 1-6 Yes 90 10 855 96 1.6Comparative Yes 100 0 848 Thermorunaway 1.6 Example 1-1 Comparative Yes85 15 853 121  1.6 Example 1-2 Comparative Yes 50 50 855 Thermorunaway1.6 Example 1-3 Comparative Yes 20 80 852 Thermorunaway 1.6 Example 1-4Comparative Yes 0 100 850 Thermorunaway 1.6 Example 1-5 Comparative No95 5 851 Thermorunaway 1.6 Example 1-6

As shown in Table 1, with respect to the batteries of Examples 1-1 to1-6, the surface maximum attained temperature at the time of conductingthe safety test by nail piercing was low as not higher than 100° C. Onthe other hand, with respect to the batteries of Comparative Examples1-1 to 1-6, the surface maximum attained temperature exceeded 100° C.,or thermorunaway was caused.

With respect to the battery of Comparative Example 1-1, it may bethought that since the proportion of polyethylene was 100%, though theshutdown function worked, the temperature reached the start temperatureof heat shrinkage of the separator, and an internal short circuit wasgenerated, leading to thermorunaway. With respect to the batteries ofComparative Examples 1-3 to 1-5, it may be thought that since shutdowndid not occur, thermorunaway was caused. With respect to the battery ofComparative Example 1-2, it may be thought that since the shutdowntemperature was high, the temperature reached a high temperature. Withrespect to the battery of Comparative Example 1-6, it may be thoughtthat since the polymeric support was not formed, adhesion between theelectrode and the separator did not occur, and the separator was easy tocause heat shrinkage.

It was noted from the foregoing fact that when not only the polymericsupport is disposed between the separator and at least one of thepositive electrode and the negative electrode, but the separatorcontains polyethylene as a main component and contains not more than 10%by mass of polypropylene, a battery in which heat shrinkage of theseparator is suppressed and which has high heat resistance and highsafety is obtained.

Examples 2-1 and 2-2

Secondary batteries of these Examples were each prepared by repeatingthe same operations as in Example 1-1, except for changing the pouringamount so as to have the amount of electrolytic solution as shown inTable 2.

Example 2-3

A secondary battery of this Example was prepared by repeating the sameoperations as in Example 1-1, except for changing the pouring amount soas to have the amount of electrolytic solution as shown in Table 2 andnot conducting heating after pouring the electrolytic solution.

Comparative Examples 2-1 to 2-3

Secondary batteries of these Comparative Examples were each prepared byrepeating the same operations as in Example 1-1, except for not formingthe polymeric support layer and changing the pouring amount so as tohave the amount of electrolytic solution as shown in Table 2.

Comparative Example 2-4

A secondary battery of this Comparative Example was prepared byrepeating the same operations as in Example 1-1, except for changing thepouring amount so as to have the amount of electrolytic solution asshown in Table 2 and not conducting heating after pouring theelectrolytic solution.

Comparative Examples 2-5 and 2-6

Secondary batteries of these Comparative Examples were each prepared byrepeating the same operations as in Example 1-1, except for changing thepouring amount so as to have the amount of electrolytic solution asshown in Table 2.

Comparative Examples 2-7 and 2-8

Secondary batteries of these Comparative Examples were each prepared byrepeating the same operations as in Example 1-1, except for changing thecell volume as well as the pouring amount so as to have the amount ofelectrolytic solution as shown in Table 2.

<Initial Discharge Capacity and Capacity Retention Rate>

Each of the secondary batteries of Examples 1-1 and 2-1 to 2-3 andComparative Examples 2-1 to 2-8 was subjected to constant-currentconstant-voltage charge at 23° C. and 200 mA for 7 hours until itreached an upper limit of 4.2 V and then subjected to constant-currentdischarge at 100 mA until it reached a final voltage of 2.5 V, therebydetermining an initial discharge capacity.

Thereafter, each of the secondary batteries was subjected to 300 cyclesof charge and discharge in such a manner that constant-currentconstant-voltage charge was carried out at 23° C. and 500 mA for 2 hoursuntil it reached an upper limit of 4.2 V and that constant-currentdischarge was subsequently carried out at 500 mA until it reached afinal voltage of 2.5 V. There was thus determined a capacity retentionrate at the 300th cycle when a discharge capacity of the first cycle atthe discharge at 500 mA was defined as 100%. The initial dischargecapacity and the capacity retention rate at the 300th cycle are shown inTable 2.

<Measurement of Weight of Electrolytic Solution in Battery>

Each of the secondary batteries of Examples 1-1 and 2-1 to 2-3 andComparative Examples 2-1 to 2-8 was measured for a weight of theelectrolytic solution in the battery.

That is, with respect to each secondary battery, after measuring aweight of the battery, the battery element is taken out and thendisassembled into the positive electrode, the negative electrode and theseparator. Thereafter, the positive electrode, the negative electrode,the separator and the exterior member are immersed in a dimethylcarbonate solution for 2 days; and after filtration, vacuum drying iscarried out for 3 days. The weight of the electrolytic solution wasobtained by subtracting the weight after vacuum drying from the initialweight. The obtained results are shown in Table 2.

<Liquid Leakage Test>

The secondary batteries of Examples 1-1 and 2-1 to 2-3 and ComparativeExamples 2-1 to 2-8 were each subjected to a liquid leakage test.

First of all, ten of each of the secondary batteries of Examples 1-1 and2-1 to 2-3 and Comparative Examples 2-1 to 2-8 were prepared, and a holehaving a diameter of 0.5 mm was bored on the exterior member 30A,followed by pressing under a pressure of 5 MPa. On that occasion, thenumber of batteries from which the electrolytic solution leaked wasdetermined. The obtained results are shown in Table 2.

TABLE 2 Presence or Liquid absence Amount of amount Initial CapacityNumber of Cell electrolytic per discharge retention of polymeric volumesolution cm3 capacity rate liquid support (cm3) (g) (g) (mAh) (%)leakage Example 1-1 Yes 6.0 1.6 0.27 852 87 0/10 Example 2-1 Yes 6.0 0.90.15 847 85 0/10 Example 2-2 Yes 6.0 2.1 0.35 854 89 0/10 Example 2-3Yes 6.0 1.6 0.27 843 78 1/10 Comparative No 6.0 1.5 0.26 852 53 9/10Example 2-1 Comparative No 6.0 2.2 0.37 849 69 10/10  Example 2-2Comparative No 6.0 2.7 0.45 849 81 10/10  Example 2-3 Comparative Yes6.0 2.3 0.38 844 82 10/10  Example 2-4 Comparative Yes 6.0 0.8 0.13 85264 0/10 Example 2-5 Comparative Yes 6.0 2.2 0.37 851 84 5/10 Example 2-6Comparative Yes 9.0 1.2 0.13 1260 59 0/10 Example 2-7 Comparative Yes5.0 2.0 0.40 709 85 6/10 Example 2-8

As shown in Table 2, in the secondary batteries of Examples 1-1 and 2-1to 2-3, the cycle characteristic was excellent, and the liquid leakagewas not confirmed or scarcely observed. On the other hand, in thesecondary battery of Comparative Example 2-1, the cycle characteristicwas poor, and the number of liquid leakage was large.

Also, in the batteries of Comparative Examples 2-5 and 2-7, the cyclecharacteristic was poor; and in the batteries of Comparative Examples2-2, 2-3, 2-4, 2-6 and 2-8, the number of cells which caused liquidleakage was large. In the battery of Comparative Example 2-1, it may bethought that because of the matter that the polymeric support layer wasnot formed, the separator and the electrode did not come into closecontact with each other; the electrolytic solution was not uniformlyspread, whereby a portion where the electrolytic solution wasexcessively present and a portion where the electrolytic solution wasshort were generated; and therefore, the cycle characteristic was poor,and the number of cells which caused liquid leakage was large.

Also, in the batteries of Comparative Examples 2-2 and 2-3, though thepolymeric support layer was not formed, the cycle characteristic wasgood because an excess of the electrolytic solution was added; however,it may be thought that the number of cells which caused liquid leakagewas large because the excessive electrolytic solution was generated.Similarly, in the battery of Comparative Example 2-4, the electrode andthe separator were not sufficiently adhered to each other becauseheating was not performed, and the cycle characteristic was good becausean excess of the electrolytic solution was added; however, it may bethought that the number of cells which caused liquid leakage was largebecause the excessive electrolytic solution was generated.

Similarly, in the batteries of Comparative Examples 2-5 and 2-7, it maybe thought that the cycle characteristic was lowered because theelectrolytic solution was short; and in the batteries of ComparativeExamples 2-6 and 2-8, it may be thought that the number of cells whichcaused liquid leakage was large because the excessive electrolyticsolution was generated.

Also, in the battery of Example 2-3, a cell which caused liquid leakagewas slightly confirmed. It may be thought that this was caused due tothe matter that the electrode and the separator were not sufficientlyadhered to each other because heating was not performed.

It was noted from the foregoing facts that when a prescribed polymericsupport is arranged between the separator and the positive electrodeand/or the negative electrode, and the amount of the non-aqueouselectrolytic solution existing within the battery is from 0.14 g to 0.35g per cm3 of the battery volume, the battery is excellent in cyclecharacteristic and has resistance to liquid leakage. Also, it was notedthat what the polymeric support is adhered to the separator and at leastone of the positive electrode and the negative electrode is morepreferable.

As shown in Examples 1-1 and 2-1 to 2-3, in the non-aqueous electrolytesecondary battery provided with a polymeric support, when the amount ofthe non-aqueous electrolytic solution existing within the battery isfrom 0.14 g to 0.35 g per cm3 of the battery volume, prescribed initialcharge-discharge capacity and capacity retention rate can be secured,and the liquid leakage can be suppressed.

In particular, in the non-aqueous electrolyte secondary battery in whichthe polymeric support is brought into close contact with or adhered toat least one of the separator, the positive electrode and the negativeelectrode, the liquid leakage can be surely avoided, and both theperformance and the safety can be made compatible with each other withinthe range of the amount of the non-aqueous electrolytic solution atwhich the battery performance is most exhibited.

In the case where the polymeric support layer is not formed as shown inComparative Examples 2-1 to 2-3, or in the case where the polymericsupport is not brought into close contact without being heated as inExample 2-3 and Comparative Example 2-4, as the amount of thenon-aqueous electrolytic solution per cm3 of the battery volumeincreases, the capacity retention rate is enhanced. However, as shown inExamples 1-1 and 2-1 to 2-2 and Comparative Examples 2-5 to 2-8, in thenon-aqueous electrolyte battery with which the polymeric support layeris brought into close contact, even when the amount of the non-aqueouselectrolytic solution per cm3 of the battery volume is increased to 0.37g or 0.40 g, the capacity retention rate is not enhanced, and theinitial discharge capacity is lowered. Also, the liquid leakage can besurely avoided in the range of the amount of the non-aqueouselectrolytic solution where all of the initial discharge capacity andthe capacity retention rate are favorable (from 0.14 g to 0.35 g percm3).

In the light of the above, when the polymeric support is brought intoclose contact with or adhered to at least one of the separator, thepositive electrode and the negative electrode, the battery performanceis most exhibited by a small amount of the non-aqueous electrolyticsolution. Also, the liquid leakage can be surely avoided, and both theperformance and the safety can be made compatible with each other withinthe foregoing range.

In the foregoing embodiment, the case where the battery element 20prepared by laminating and winding the positive electrode 21 and thenegative electrode 22 is provided has been described. However, in thecase where a tabular battery element in which a pair of a positiveelectrode and a negative electrode is laminated, or a laminate typebattery element in which plural positive electrodes and negativeelectrodes are laminated is provided, the present invention can also beapplied. Also, the present invention can be applied to not only asecondary battery but a primary battery.

Furthermore, as described previously, the present invention is concernedwith a battery using lithium as an electrode reactant. However, thetechnical thought can also be applied to the case of using other alkalimetal such as sodium (Na) and potassium (K), an alkaline earth metalsuch as magnesium (Mg) and calcium (Ca) or other light metal such asaluminum.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

1. A non-aqueous electrolyte secondary battery comprising: a positiveelectrode; a negative electrode; a separator disposed between thepositive electrode and the negative electrode; a non-aqueouselectrolytic solution; and an exterior member made of a laminatematerial and housing the positive electrode, the negative electrode, theseparator and the non-aqueous electrolytic solution, wherein a polymericsupport exists between the separator and at least one of the positiveelectrode and the negative electrode; and the separator containspolyethylene as a main component and contains not more than 10% by massof polypropylene.
 2. The non-aqueous electrolyte secondary batteryaccording to claim 1, wherein the non-aqueous electrolytic solutionexisting in the non-aqueous electrolyte secondary battery is from 0.14to 0.35 g per cm3 of the volume of the non-aqueous electrolyte secondarybattery.
 3. The non-aqueous electrolyte secondary battery according toclaim 1, wherein the polymeric support comes into close contact with oradheres to the separator and at least one of the positive electrode andthe negative electrode.
 4. The non-aqueous electrolyte secondary batteryaccording to claim 1, wherein the polymeric support contains a polymercontaining vinylidene fluoride as a constitutional component.
 5. Thenon-aqueous electrolyte secondary battery according to claim 1, whereinthe non-aqueous electrolytic solution contains a halogen atom-containingcyclic carbonic ester derivative.
 6. The non-aqueous electrolytesecondary battery according to claim 5, wherein the cyclic carbonicester contains at least one of 4-fluoro-1,3-dioxolan-2-one and4-chloro-1,3-dioxolan-2-one.
 7. The non-aqueous electrolyte secondarybattery according to claim 1, wherein the separator has a thickness offrom 5 to 20 μm.
 8. The non-aqueous electrolyte secondary batteryaccording to claim 1, wherein the laminate material constituting theexterior member is composed of aluminum and a resin.